Both the 3G and WiFi ordering pages now come with this new note: "Due to strong customer demand, Kindle is temporarily sold out. Shipments will be prioritized on a first-come, first-serve basis." Naturally, the e-retailer didn't give an indication of how many devices on pre-order it took to reach that sellout milestone, but the fact that it happened so quickly does demonstrate how the word "Kindle" has become increasingly synonymous with e-books.

Amazon's competitors, however, are hardly down for the count. Barnes & Noble (BKS) announced last week that many of its brick-and-mortar stores would feature 1,000-square foot "full service" boutiques showing off its own e-reader, the Nook, whose 3G and WiFi models are priced at $199 and $149, respectively. Barnes & Noble has a lot riding on its digital book business and has been spending money accordingly, and it appears to be paying off in the form of 33% market share as of late July, according to Digitimes Research. Meanwhile, the presence of the competing iBooks platform for Apple's (AAPL) iPad and iPhone hasn't prevented Amazon from increasing its own e-book sales count on those devices either.

While keeping the Kindle's price artificially low and losing money per unit is all part of Amazon's greater business plan,The Wall Street Journal's Martin Peers wondered if this tactic "risks scaring those who don't trust the company's commitment to the bottom line." But Amazon's moves bolster a deeper commitment from its customers, who will continue to buy e-books in such a way that allows books like Stieg Larsson's Millennium Trilogy to sell over a million Kindle editions. The company's recent actions are also warning shots, signaling to its competitors that any move they make -- such as dropping e-reader prices below $100 -- Amazon will match, and then better.

So to the anxious and the nervous: Sit back, relax and enjoy the continuing digital book developments. There will be far more of them, and there's still room for some late-game surprises.